rogerthebodger
Well-Known Member
As VicS posted galvanizing (hot dip) is alloyed with the under lying steel and you will only get any corrosion of the underlying steel if there is a break in the galvanizing.
I have a steel boat and all the structure inside was galvanized before final installation. This did include some cutting and drilling of holes with stainless steel bolts.
In over 10 years of use there is no noticeable of any corrosion (galvanic or oxidation ) of any or the inter structurer. The zinc of the galvanizing does protect the steel but you do get some oxidation but very little .
Stainless steel welded to mild steel yes welded also does not show any galvanic corrosion. The junction does need to be protected by paint and if that paint cracks you can get oxidation to the underlying mild steel.
I have lots of stainless steel welded to mild steel I also have some welded stainless /mild steel that has been subsequently galvanized with no corrosion of either type.
If you weld to galvanized steel you will burn off the galvanizing and expose the mild steel and thus get corrosion.
Galvanic corrosion is different to oxidation (rust is one type) and occur under different conditions. oxidation needs plenty of oxygen mainly in air but can be under water as here is dissolved oxygen in water both sea and fresh.
Galvanic corrosion needs dissimilar metals electrically connected and immersed in am electrolyte.
Break any one any you eliminate Galvanic corrosion but you can still get oxidation of the steel either ( Fe3O4) or (Fe2O3).
You can get away with stainless steel welded to mild steel as they are close on the galvanic scale.
All my skin fittings both above and below the water line are 316 stainless steel properly sealed to prevent crevice corrosion. some steel boat have a stainless steel half nipple welded to the mild steel hull as a skin fitting with a stainless steel ball valve screwed to the half nipple
Any erosion of the zinc in the galvanizing will be very very slow due to the much larger area of any galvanizing compared to the area of any stainless steel
I have a steel boat and all the structure inside was galvanized before final installation. This did include some cutting and drilling of holes with stainless steel bolts.
In over 10 years of use there is no noticeable of any corrosion (galvanic or oxidation ) of any or the inter structurer. The zinc of the galvanizing does protect the steel but you do get some oxidation but very little .
Stainless steel welded to mild steel yes welded also does not show any galvanic corrosion. The junction does need to be protected by paint and if that paint cracks you can get oxidation to the underlying mild steel.
I have lots of stainless steel welded to mild steel I also have some welded stainless /mild steel that has been subsequently galvanized with no corrosion of either type.
If you weld to galvanized steel you will burn off the galvanizing and expose the mild steel and thus get corrosion.
Galvanic corrosion is different to oxidation (rust is one type) and occur under different conditions. oxidation needs plenty of oxygen mainly in air but can be under water as here is dissolved oxygen in water both sea and fresh.
Galvanic corrosion needs dissimilar metals electrically connected and immersed in am electrolyte.
Break any one any you eliminate Galvanic corrosion but you can still get oxidation of the steel either ( Fe3O4) or (Fe2O3).
You can get away with stainless steel welded to mild steel as they are close on the galvanic scale.
All my skin fittings both above and below the water line are 316 stainless steel properly sealed to prevent crevice corrosion. some steel boat have a stainless steel half nipple welded to the mild steel hull as a skin fitting with a stainless steel ball valve screwed to the half nipple
Any erosion of the zinc in the galvanizing will be very very slow due to the much larger area of any galvanizing compared to the area of any stainless steel
